1. Field of the Invention
The present invention relates to a wired circuit board to connect with a suspension board with circuit equipped with a magnetic head of a hard disk drive.
2. Description of the Prior Art
In the hard disk drive, the suspension board with circuit equipped with the magnetic head usually has lines for transmitting read signals and write signals to the magnetic head. These lines are connected to terminal portions of the wired circuit board equipped with an electronic device such as a preamplifier IC. The signals from the lines are amplified by the electronic device such as the preamplifier IC placed on the wired circuit board and then transmitted from the wired circuit board to a control circuit board for controlling the magnetic head.
Meanwhile, along with improvement in recent years to fine pitch wiring and to high frequency signal, it is increasingly becoming necessary to control characteristic impedances at connection points between the lines of the suspension board with circuit and the terminal portions of the wired circuit board connected thereto.
If there is inconsistency in characteristic impedance at the connection points, transmission efficiency of the signal will be reduced. Particularly, the signal before input to the preamplifier IC (the signal before amplified) is so weak that it is easily influenced by the characteristic impedance at the connection points, so that the transmission efficiency of the signal is reduced easily.
For example, U.S. Pat. No. 5,712,749 proposes improvement of this suspension board with circuit, according to which an opening is formed in the stainless board at a location under the wires, to optimize the capacitance of the signal, so as to control the characteristic impedance.
This proposed construction can control the characteristic impedance of the suspension board with circuit itself, but it cannot control the characteristic impedances at the connection points between the lines of the suspension board with circuit and the terminal portions of the wired circuit board connected thereto. Accordingly, the problem of the reduction in transmission efficiency at the connection points remains unavoidable.